PowerPCReview

Revision 1 as of 2006-11-10 02:22:48

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Summary

PowerPC, already a significantly less mainstream architecture than x86(-64), has seen it's visibility further reduced by the fact that Apple, the primary source of consumer PowerPC hardware, has moved away from the platform. Ubuntu needs to decide whether PowerPC should continue as a fully supported platform for the feisty release.

Rationale

  • Reasons against keeping PowerPC as a fully supported architecture:
    • In July 2005, PowerPC represented 1.95% of downloads from archive.ubuntu.com. In only 15 months (i.e. to November 2006) that number has declined to 0.8%.
    • In January of 2006 Apple started switching from PowerPC to Intel and by August 2006 its entire consumer line had switched away from the PowerPC architecture. That leaves people with (as good as) no access to new consumer level desktop or laptop PowerPC based hardware.
    • PowerPC represented 3.3% of CD downloads from releases.ubuntu.com for dapper but only 2.7% of CD downloads for edgy.
    • Testing an Ubuntu release involves a complex testing process that currently involves testing 22 variations for each architecture. Fully supporting PowerPC means the full 22 variations have to be tested which is a strain on available resources especially since testing requires physical access to hardware, much of which is no longer on sale.
    • archive.ubuntu.com and releases.ubuntu.com are mirrored by hundreds of mirrors worldwide. Each architecture increases the total size of the archive and the size of updates sent to all these mirrors everyday.
      • Overall size of PowerPC on archive.ubuntu.com: 27Gb (15% of total size)
      • Overall size of PowerPC on releases.ubuntu.com: 9.2Gb (32% of total size)
    • PowerPC currently provides no production-level virtualization support to the degree we require for PPA (PersonalPackageArchives) or Grumpy. This makes it harder for community members without access to PowerPC hardware to support the port.

    • Several of the PowerPC specific tools (e.g. yaboot) are essentially unmaintained and trying to keep them (and the PowerPC) port current with new technologies (e.g. gfxboot) is difficult and time consuming.
  • Reasons for keeping PowerPC as a fully supported architecture:
    • When Apple EOL support for their PowerPC based machines, there'll be several knock on effects:
      • Existing Apple users may choose to migrate to Ubuntu so they can continue to use a supported OS
      • Existing Ubuntu users may be able to pick up second hand PowerPC hardware very cheaply
        • Both of these may lead to an increase in demand for the PowerPC port.
    • Sony's PS3 is PowerPC based and will support running Linux
    • IBM's OpenPower platform ensures that powerpc remains a viable Linux platform on the server

    • There are some existing IHVs (e.g Genesi) producing powerpc based consumer hardware
    • [http://www.power.org/ power.org] exist to try encourage further IHV powerpc based consumer hardware

    • Xen is being worked on, however it requires hardware assist and only certain types of PowerPC hardware are suitable (notably, Apple Hardware and OpenPOWER servers are not).

Use cases

Scope

This specification is limited in scope in the following ways:

  • It only considers the future of the PowerPC port for the feisty release. This specification will need to be revisited for feisty+1.
  • Removal of the PowerPC port entirely is not under consideration.

Design

Implementation

There are three possible alternative implementations:

  • PowerPC remains a fully supported platform
  • PowerPC becomes a 'supported on the server only' platform (like Sparc)
  • PowerPC becomes a community supported platform (like PA-RISC and Itanium)

Code

Data preservation and migration

If PowerPC becomes a community supported platform and moves to ports.ubuntu.com, there will be some some migration issues.

  • Migration of feisty only for PowerPC to ports.ubuntu.com while retaining edgy and earlier releases on archive.ubuntu.com

  • Changes necessary to debian-installer and other packages to adjust for powerpc being on ports.ubuntu.com rather than archive.ubuntu.com

The former is complicated by the fact that the current archive/ports split is achieved by a simple list of rsync exclude and includes. If feisty PowerPC moves to ports.ubuntu.com, the split process would have to become signficantly more intelligent (e.g. by parsing the Packages and Sources files to determine what files need to be copied across and/or excluded).

Unresolved issues

The fundamental decision remains undecided.

BoF agenda and discussion


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